The field of the invention relates to engine control systems, including air/fuel ratio control systems, which provide rapid warm-up of the catalytic converter.
U.S. Pat. No. 5,483,946 describes a system in which robust cold-start air/fuel ratio (A/F) control was accomplished by utilizing a "cold" adaptive A/F table to schedule A/F values during the open-loop period following any engine start in which the engine coolant temperature (ECT) is within a certain prescribed range. In that system, the cold adaptive A/F table is updated whenever the engine operates in closed-loop A/F operation while the ECT is in the prescribed range. Updating of the cold adaptive continues until the ECT exceeds a certain value. When this occurs, the engine reverts to normal A/F feedback control, although the "hot" adaptive table would not be updated until the engine had fully warmed up. Once the engine has warmed up, the hot adaptive table would be updated. If an engine start occurred when the ECT was below the prescribed temperature, the open-loop A/F at any rpm/load point would be scheduled based on an extrapolation of values in the cold and hot adaptive tables as a function of ECT. If an engine start occurred when the ECT was above the prescribed temperature but below the fully warmed up temperature, the base A/F at any rpm/load point would be scheduled based on an interpolation of values in the cold and hot adaptive tables as a function of ECT. The system described in U.S. Pat. No. 5,483,946 does not account for changes in operating characteristics during warmed up operation which may affect the cold adaptive table.
For example, the cold A/F adaptive table could produce erroneous A/F values if the vehicle was refueled with a different fuel after the cold adaptive table had been "programmed" for the next engine cold start. In particular, different fuels can produce different system characteristics which the A/F control strategy must learn and subsequently adapt for. This is an ongoing problem since there is a large variety of available fuels which consumers can arbitrarily select and switch between. Furthermore, these fuels can behave differently for both cold and hot running conditions. Thus, in this example, the next engine cold start would thus occur with a fuel having different characteristics than that represented by the cold adaptive table. Accordingly, there exists a need for a control strategy which adapts the A/F during both cold and hot engine operating conditions and, in particular, modifies the cold adaptive table in accordance with operating characteristics occurring during hot engine operation.